The superconducting quantum interference fluxmeter is a superhigh-sensitivity fluxmeter using a superconducting quantum interference device, generally known as "SQUID" (abbreviated from superconducting quantum interference device). It utilizes the characteristic of the SQUID (a superconducting ring containing a weak superconducting part) to make cyclic responses to magnetic flux by increments of one flux quantum (.phi..sub.o =2.07.times.10.sup.-15 Weber).
As shown above, one flux quantum is a very small unit. But magnetic fluxes as weak as approximately 1/1000 flux quantum are measured by use of suitable measuring circuits. Magnetic flux can be related with electric current and voltage, using inductance and resistance. Therefore, the SQUID fluxmeter may be used as an ammeter and a voltmeter, too.
The SQUID is a device that captures and releases flux quantum into and out of a superconducting ring having a weak superconducting part, as controlled by application of electric current or magnetic field from outside. With this feature, it is becoming apparent that the SQUID may be utilized also as an electronic circuit device needed for large-capacity, subminaiture and high-speed information processing machines used as ultra-low temperatures.